feat: run commands to get settings

src/scriv/config.py

@@ -13,6 +13,7 @@
 from .exceptions import ScrivException
 from .literals import find_literal
 from .optional import tomllib
+from .shell import run_shell_command
 
 logger = logging.getLogger(__name__)
 
@@ -363,6 +364,7 @@ def resolve_value(self, value: str) -> str:
         Prefixes:
             "file:" read the content from a file.
             "literal:" read a literal string from a file.
+            "command:" read the output of a shell command.
 
         """
         value = value.replace("${config:format}", self._options.format)
@@ -392,6 +394,14 @@ def resolve_value(self, value: str) -> str:
                     + f"{value!r}"
                 )
             value = found
+        elif value.startswith("command:"):
+            cmd = value.partition(":")[2].strip()
+            ok, out = run_shell_command(cmd)
+            if not ok:
+                raise ScrivException(f"Command {cmd!r} failed:\n{out}")
+            if out.count("\n") == 1:
+                out = out.rstrip("\n")
+            value = out
         return value
 
     def read_file_value(self, file_name: str) -> str:

src/scriv/shell.py

@@ -46,3 +46,19 @@ def run_simple_command(cmd: Union[str, List[str]]) -> str:
     if not ok:
         return ""
     return out.strip()
+
+
+def run_shell_command(cmd: str) -> CmdResult:
+    logger.debug(f"Running shell command {cmd!r}")
+    proc = subprocess.run(
+        cmd,
+        shell=True,
+        check=False,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+    )
+    output = proc.stdout.decode("utf-8")
+    logger.debug(
+        f"Command exited with {proc.returncode} status. Output: {output!r}"
+    )
+    return proc.returncode == 0, output

tests/faker.py

@@ -11,7 +11,7 @@
 
 class FakeRunCommand:
     """
-    A fake implementation of run_command.
+    A fake implementation of run_command and similar functions.
 
     Add handlers for commands with `add_handler`.
     """
@@ -22,9 +22,9 @@ def __init__(self, mocker):
         self.mocker = mocker
         self.patch_module("scriv.shell")
 
-    def patch_module(self, mod_name: str) -> None:
+    def patch_module(self, mod_name: str, func_name: str = "run_command") -> None:
         """Replace ``run_command`` in `mod_name` with our fake."""
-        self.mocker.patch(f"{mod_name}.run_command", self)
+        self.mocker.patch(f"{mod_name}.{func_name}", self)
 
     def add_handler(self, argv0: str, handler: CmdHandler) -> None:
         """

tests/test_config.py

@@ -344,3 +344,31 @@ def test_no_toml_installed_no_settings(self, temp_dir):
         with without_module(scriv.config, "tomllib"):
             config = Config.read()
         assert config.categories[0] == "Removed"
+
+
+def test_command_running(fake_run_command):
+    # Any setting can be the output of a command.
+    fake_run_command.patch_module("scriv.config", "run_shell_command")
+    fake_run_command.add_handler(
+        "showtext", lambda argv: (True, " ".join(argv[1:]))
+    )
+    text = Config(output_file="command: showtext Xyzzy 2 3").output_file
+    assert text == "Xyzzy 2 3"
+
+
+def test_real_command_running():
+    text = Config(output_file="command: echo Xyzzy 2 3").output_file
+    assert text == "Xyzzy 2 3"
+
+
+@pytest.mark.parametrize(
+    "bad_cmd, msg_rx",
+    [
+        ("xyzzyplugh", "Couldn't read 'output_file' setting: Command 'xyzzyplugh' failed:"),
+        ("'hello!2><", re.escape('Couldn\'t read \'output_file\' setting: Command "\'hello!2><" failed:')),
+    ]
+)
+def test_bad_command(fake_run_command, bad_cmd, msg_rx):
+    # Any setting can be the output of a command.
+    with pytest.raises(ScrivException, match=msg_rx):
+        Config(output_file=f"command: {bad_cmd}").output_file